1. Field of the Invention
The invention relates to a method and a device for adjusting operating parameters of a robot, and to a program and a recording medium for the method.
2. Description of the Related Art
Methods exist for adjusting operating parameters of a robot that serves to move an effector tool along a given path in an optimum cycle time.
When it is desired to minimize the cycle time, such methods are known under the term “minimum time control”.
The cycle time is the time needed by the robot to cause the effector tool to travel all the way along a given path from a starting point to a destination point, while passing via intermediate points of passage. Generally, the robot repeats the same movement several times over so that the path constitutes a closed loop where the starting point and the destination point are the same.
The operating parameters of the robot determine the accuracy with which the effector tool travels along the given path and also the speed and the acceleration of the effector tool along said path. More precisely, the operating parameters can be used by an electronic robot control unit which, on the basis of the operating parameters and of the point of passage on the given path, is capable of controlling the electric actuators of the robot so that the robot moves the effector tool along the given path. By way of example, the operating parameters are a maximum acceleration, a maximum deceleration, and a maximum speed that can be accepted over a portion of the given path, or the duration required for traveling along a portion of the path.
The operating parameters of a robot are very numerous. Furthermore, the relationships between those operating parameters and integratable operating constraints are often very complex.
The term “integratable operating constraint” is used to mean limit values for integratable physical magnitudes of the actuators of the robot. The value of each integratable physical magnitude is the result of integrating the instantaneous value of other physical magnitudes along the complete path. In other words, the values of these integratable physical magnitudes are calculated by integrating the instantaneous values of one or more other physical magnitudes of the robot between the starting point and the destination point of the given path.
By way of example, such integratable physical magnitudes are the operating temperatures of an actuator, of a lubricant, of a joint, of on-board electronic components (encoders, . . . ), . . . etc. The degree of wear of ball bearings in transmissions is likewise an integratable physical magnitude. Operating temperature and degree of wear are functions of integrating instantaneous values over the entire path, which instantaneous values are the values of other physical magnitudes such as the speed of rotation or the power supply current of an actuator.
In the description below, each operating parameter is written pj where the subscript j is an identifier of the operating parameter. A vector {right arrow over (P)} of operating parameters is also defined by the following relationship:{right arrow over (P)}=(p1; p2; . . . , pj; . . . ; pm)T where:                T is the transposition function; and        m is the number of operating parameters.        
There are control methods in existence that take account of temperature limits for robot actuators in order to adjust the operating parameters so as to achieve a minimum cycle time (see for example WO 02/074501). By way of example, the temperature limits for each actuator are defined on the basis of data supplied by the manufacturer of the actuator.
On the basis of measurements performed during a real movement of the effector tool and/or on the basis of readings delivered by a robot movement emulator, those existing methods comprise the following steps:
a) a step of determining the value of the cycle time as a function of the values of the operating parameters;
b) a step of determining the value of an operating temperature resulting from following the complete path; and
c) a step of modifying the values of the operating parameters to move the cycle time closer to its optimum value.
Steps a) to c) are reiterated so long as the cycle time can still be minimized without the operating temperature exceeding its limit value.
Typically, the cycle time and the operating temperatures vary in opposite directions. Thus, the shorter the cycle time, the higher the operating temperature of each actuator. As a result, the minimum cycle time is achieved when at least one of the operating temperatures is equal to its limit value. Existing methods thus lead systemically to causing the robot to operate with an operating temperature that is equal to its limit value. This is not desirable in all situations. For example, the following situations might be preferred:
1) adjusting the operating parameters so as to obtain a cycle time that is slightly longer than the cycle time obtained using existing methods, but with operating temperatures that are well below the limit values; and
2) adjusting the operating parameters so as to obtain a cycle time that is considerably shorter than that obtained using existing methods, even though that requires operating at an operating temperature that is slightly above the limit value.